This invention relates to an electrophotographic apparatus comprising a photosensitive and electrostatic charge retentive member including an electrically conductive substrate and a photosensitive layer applied on the substrate, a corona charger for uniformly charging the photosensitive member, an optical system for projecting image of a document to be duplicated onto the photosensitive member to form an electrostatic latent image, a device for developing the electrostatic latent image to form a toned image, and a device for transferring the toned image onto a record paper.
In conventional electrophotographic apparatus, a width of the photosensitive layer on the photosensitive member, e.g. a photoconductive drum and a photoconductive endless belt, is made wider than the maximum permissible width of the record papers, and widths of active areas of various parts such as the uniformly charging device, optical system for projecting document image onto the photosensitive layer, toning device, transferring device, cleaning device and so on. On the other hand various types of electrophotographic apparatuses have been proposed in which a peeling claw or a peeling belt is used for peeling the record paper off the photosensitive drum after the toned image on the drum has been transferred onto the record paper, while the paper is urged against the drum. For this purpose there is often provided an inwardly stepped or depressed portion in the drum at each of its side edges, into which depressed portions the peeling claws are inserted. In case of liquid development the depressed portion is also used for draining excess liquid toning or developing agent. In an electrophotographic apparatus of this kind, the photosensitive layer is easily deteriorated or made dirty at the side edges against which the peeling claws or the peeling belts are urged or through which the excess toning agent flows, so that the width of the photosensitive layer applied on the conductive substrate is generally made slightly narrower than the maximum permissible width of record papers. In such an electrophotographic apparatus the inventors have found that undesired thin lines or thick stripes might appear in side edge portions of the record paper corresponding positionally to side edges of the photoconductive layer.
Such a blackening is caused by the fact that a thickness of the photosensitive coating layer is gradually decreased at the side edges, because it is quite difficult to apply uniformly the photosensitive layer on the electrically conductive substrate. When the document image is projected onto the photosensitive layer, its inclined side edge portions are insufficiently exposed to light and thus residual charge remains thereon. Therefore electric fields of high intensity are produced at the side edges and a relatively large amount of toners is attracted along side edges. These toners are transferred to the record paper, so that there are produced on the record paper black lines or stripes along its side edges. Further it is considered that a large amount of toners is liable to adhere to the side edge portions of the photosensitive layer during the development due to a so-called edge effect.
This blackening will be explained more in detail with reference to attached drawings hereinafter.